This invention relates to passenger sensing system and method and, more particularly, to improvements in passenger sensing system and method, in which the air bag of an air bag unit installed in a car can be set to an expansible or non-expansible state according to the seated state of a passenger on an assistant's seat of the car.
The air bag unit is usually provided in the car in order to alleviate a shock exerted to a passenger in the event of collision of the car. The air bag unit is inevitable for the car safety, and it is recently installed not only in the driver's seat but also in the assistant's seat.
In FIG. 15 showing an air bag unit, the illustrated air bag comprises a squeave circuit on the driver's seat side, which is a series circuit of a safing sensor SS1, a squeave SQ1 and a semiconductor switching element SW1 such as an FET field-effect transistor, a squeave circuit on the assistant's seat, which is a series circuit of a safing sensor SS2, a squeave SQ2 and a semiconductor switching element SW2 such as an FET, an electronic acceleration sensor or shock sensor) GS, and a control circuit CC which has a function for supplying a signal to the gates of the semiconductor switching elements SW1 and SW2 by making a check, according to the output signal of the electronic acceleration sensor GS, as to whether collision has taken place.
With this air bag unit, in the event of collision of the car due to some cause, the switch contacts of the safing sensors SS1 and SS2 are closed in response to a relatively low acceleration. As a result, the squeave circuits on the driver s seat and the assistant's seat are made ready to be operated. When the control circuit CC determines according to the signal from the electronic acceleration sensor GS that collision of the car has taken place, it supplies a signal to the gates of the semiconductor switching elements SW1 and SW2 to turn on these elements. Consequently, a current is caused to pass through the squeave circuits, thus causing heat generation from the squeaves SQ1 and SQ2 and expansion of the air bags on the driver's and assistant's seats. In this way, the passengers are protected from the shock due to the collision.
According to this air bag unit, the above effect of the passenger protection in the event of the collision can be expected in the case when an adult P is seated in a seat 1, as shown in FIG. 16(a). However, in the case when a child SP is seated in a rearward-facing child seat (hereinafter referred to as RFCS) 1A which is secured to the top of an assistant's seat 1 as shown in FIG. 16(b), adverse effects of the expansion of the air bag on the child SP is anticipated. In this case, therefore, it is desirable that the air bag remains without being expanded even in the event of a collision. In another case when a child SP is seated in a forward-facing child seat (hereinafter referred to as FFCS) 1A secured to the top of an assistant's seat 1 as shown in FIG. 16(c), it is anticipated that the face of the child SP would be covered by the expanded air bag. In this case, like the case of the RFCS, it is again desirable that the air bag remains without being expanded even in the event of a collision.
To cope with the above problem, an air bag unit as shown in FIG. 17 has been proposed. This air bag unit has a sensor SD for checking whether or not a passenger is seated in the assistant's seat. In this unit, the control circuit CC checks the seated status of a passenger on the assistant's seat and, as a result of the check, sets the air bag to be in a state able or unable to be expanded. As the sensor SD has been proposed one which uses a weight sensor comprising a piezoelectric sensor for measuring the weight, and one in which a photograph of a passenger seated in a seat, taken with a camera, is processed for making a check as to whether the passenger is an adult P or a child SP, or in the case of a child SP, whether the child SP is on the FFCS or RFIS.
The former sensor permits a rough check as to whether a passenger is an adult P or a child SP and, as a result of the check, setting the air bag to the state able or unable to be expanded for evading an accident in the event of a collision. However, the person's weight varies with individuals, and a child may be heavier than an adult. Therefore, the sensor lacks accuracy. In addition, the sensor cannot check whether a child is on the RFCS OR FFCS.
The latter sensor can relatively accurately check the state of a passenger, whether the passenger is an adult P or a child SP and whether a child on the child seat is in the state of the RFCS or FFCS. However, it is necessary to photograph the passenger with a camera, process the photograph data and compare the processed data with various patterns. Therefore, a problem is posed that a complicated and expansive processor is necessary.
To cope with this problem, a passenger sensing system using an infrared sensor or an ultrasonic sensor has been proposed in, for instance, U.S. Pat. No. 5,482,314. In this passenger sensing system, an infrared sensor comprising a plurality of elements and an ultrasonic sensor are disposed above a front seat, and the seated status of a passenger on a seat is checked by checking whether the data from these sensors have a temperature pattern and an ultrasonic pattern corresponding to the seated status of a passenger on a seat (such as a seated adult, a child on the RFIS or vacant seat).
This proposed system can make a check with considerable accuracy under particular conditions as to whether a passenger is present owing to combined effects of the infrared and ultrasonic sensors. However, the system has a problem that the accuracy of detection is adversely affected by ambient conditions and unstable. Specifically, when the car room is cooled so that cool air is in contact with the passenger s face and the like, the passenger's surface temperature is reduced so that the result of detection of the infrared sensor does not always correspond to the body temperature. In addition, when the ambient temperature is close to the body temperature, the ambient temperature and the body temperature can not be discriminated from each other from the result of detection of the infrared sensor. Under such a condition, proper judgment can not be obtained by comparing the detection data from the infrared sensor and a reference temperature pattern data corresponding to various seated states of passengers or the like. With such adverse effects of the ambient conditions, accurate and stable passenger detection cannot be expected, and the air bag cannot be properly controlled.